Number of accounts > 65,536 in a single server ?

[Heman Lu]

Hi,

        I'm planning to migrate our mail server from sendmail
        to qmail. There are 55,000+ mail accounts. When simulating
        to grow beyond 65,536 accounts, I encounter some problems.

        Here is my test environment:

                Hardware: Acer Altos 12000
                          -- Pentium III 450 x 2
                          -- 1 GB DRAM
                          -- IBM Ultra2 SCSI Disk 9GB x 7 (as RAID 5)

                Software: RedHat Linux 6.1
                          -- With shadow passwd
                          -- qmail 1.0.3

        The major problem is for all the accounts with UID larger
        than 65,535 are invalid when chown, su or checkpassword for
        qmail-pop3d. But I still can do getpwnam and getpwent perfectly
        by Perl or C. There is no such a problem in Solaris 2.6.

        I know it's a crazy idea to put tens of thousands accounts in
        a single box. But it should work. Performance is acceptable 
        if seperating mail queues to another machine in my experience. 
        So I'm curious whether there are any tricks to fix the problem?

        Any advice for better scalability is also welcome and highly
        appreciated.

        Cheers,
        Heman Lu